This invention relates to a mobile radio communication apparatus and, in particular, to a control technique of controlling a transmission output of a mobile radio communication apparatus used in a TDMA (Time Division Multiple Access) mobile radio communication system.
Generally, in a pan-European mobile telephone system GSM (Global System for Mobile communication), it is attempted to reduce the size of a communication cell (communication area) in order to enhance communication traffic. In a mobile communication apparatus, it is required to reduce an output of a transmission power. If the communication cell is reduced in size a high transmission output would result in a widened dynamic range of transmission output control. In case of a xe2x80x9ctransmission power sensing systemxe2x80x9d which has been adopted, this results in expansion of a dynamic range of a detector. As a consequence, it is difficult to detect the transmission output used upon transmission output control.
Typically, the detector comprises a single diode. It is difficult for such detector to cover a detection range of the transmission output Therefore, instead of the control system for detecting the transmission output to perform feedback control, use is also made of a control system for detecting an electric current flowing into a current amplifying circuit to perform feedback control upon the current amplifying circuit.
In such a transmission current sensing system, it is difficult to compensate the variation in power amplifier efficiency at different conditions (for example, temperature, power supply voltage channel frequency). Under the circumstances, the mobile radio communication apparatus is provided with a memory table for software-based correction of the transmission output. However, if the transmission output is corrected by the use of the memory table, the number of items in adjustment upon manufacture of the mobile radio communication apparatus is increased. In addition, a large-capacity memory is required.
It is an object of this invention to provide a mobile radio communication apparatus which is capable of readily correcting a transmission output.
According to this invention, there is provided a mobile radio communication apparatus comprising:
a control section for producing a baseband transmission signal and a transmission ramp production signal having a ramp waveform;
a radio section for converting the baseband transmission signal into a radio frequency transmission signal;
a power amplifier supplied with the radio frequency transmission signal for power-amplifying the radio frequency transmission signal into an amplified transmission signal which is transmitted through an antenna, the power amplifier having a dynamic range controlled with reference to the amplified transmission signal;
first detecting means having a first detection sensitivity and responsive to the amplified transmission signal for detecting the amplified transmission signal at the first detection sensitivity to produce a first output voltage signal;
second detecting means having a second detection sensitivity lower than the first detection sensitivity and responsive to the amplified transmission signal for detecting the amplified transmission signal at the second detection sensitivity to produce a second output voltage signal;
combining means for combining the first output voltage signal with the second output voltage signal to produce a combined output signal; and
comparing means supplied with the combined output signal for comparing the combined output signal with the transmission ramp production signal to produce a comparison result signal and for controlling the dynamic range of the power amplifier with reference to the comparison result signal.
The first detecting means comprises high-sensitivity detecting means for high-sensitivity detecting the amplified transmission signal to obtain a high-sensitivity detection signal and voltage limiting means for limiting a voltage of the high-sensitivity detection signal to a predetermined voltage to produce the first output voltage signal.
The voltage limiting means comprises a diode connected in parallel to the high-sensitivity detecting means.
The second detecting means comprises low-sensitivity detecting means for low-sensitivity detecting the amplified transmission signal to obtain a low-sensitivity detection signal and offset voltage superposing means for superposing a predetermined offset voltage upon the low-sensitivity detection signal to produce the second output voltage signal.
The offset voltage superposing means comprises an offset voltage source to produce the predetermined offset voltage, resistor means connected to an output of the low-sensitivity detecting means and to the offset voltage source to produce the low-sensitivity detection signal with the predetermined offset voltage superposed thereon, and operational amplifier means responsive to the low-sensitivity detection signal with the predetermined offset voltage superposed thereon for obtaining the second output voltage signal.
The comparing means comprises a comparator for comparing the combined output signal with the transmission ramp production signal to produce the comparison result signal which is supplied to a power control terminal of the power amplifier so that the dynamic range of the power amplifier is controlled with reference to the comparison result signal.